fix: mock github checks in tests

src/jest.setup.ts

@@ -1,5 +1,24 @@
 import failOnConsole from 'jest-fail-on-console';
 
+// Polyfill fetch for the Node.js test environment.
+// Jest runs tests inside a VM context where the global `fetch` is not
+// automatically provided, even on Node 18+. Octokit requires a `fetch`
+// implementation, so we provide one using undici's implementation.
+// This ensures tests that interact with Octokit do not throw when
+// constructing the client.
+import { fetch, Headers, Request, Response } from 'undici';
+
+if (!global.fetch) {
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (global as any).fetch = fetch;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (global as any).Headers = Headers;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (global as any).Request = Request;
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (global as any).Response = Response;
+}
+
 // Fail when console logs something inside a test - use spyOn instead
 failOnConsole({
   shouldFailOnWarn: true,